DE10161918C2 - Method for operating a level sensor and level sensor - Google Patents

Description

Technical field

Level sensors today are used to determine the level of fluids in containers ren used, which transmit signals to display units, which the detected Fluid level. The level sensor can e.g. B. as a structure of two comb interdigitated electrodes can be formed, the capacity being the measured variable between the two electrodes. Depending on the degree of coverage of the two electrodes through the fluid, a capacity is established, which with known dielectric con constant of the fluid used to determine the level of the fluid in the container can be.

State of the art

The determination of fill level with a capacitive sensor is based on the determiner capacitance between electrodes. An increase in the meaningfulness of the received A measurement signal can be achieved by having the same on both sides of a carrier Electrode structures are applied, and opposing electrodes be short-circuited. With the opposite arrangement of electrodes on a ge However, the common carrier substrate is associated with the disadvantage that parasitic capacitances occur, the measurement of the capacities of the two electrical associated with the carrier that can falsify. The electric field lines run in almost equal parts through the medium and the medium. The parasitic capacitances that occur are also not constant, but change over time, i.e. H. are dependent on aging of the level sensor. Furthermore, the parasitic capacitances that occur are dependent on the temperature and shift with this. In this context, the Expression used temperature drift.  

Furthermore, with level sensors that work according to the principle of capacitance measurement Large measurement errors occur when condensation forms inside the container Water does not appear or the level sensor does not freeze above the level can be completely excluded. The dielectric constant of water is opposite that of oil increased about 16 times. When measuring using the capacitive Level sensor, however, is based on the known dielectric constant of the fluid gone, whose level needs to be determined. It is obvious that fogging through water or the formation of icing on the level sensor, which he averaged measured values falsified until unusable. If one after the capaci principle working level sensor on an internal combustion engine for determination oil level in the oil pan can be used with the previous capacitive filling level sensors z. B. from a defective cylinder head gasket entering the oil pan, which affects the level sensor due to fogging, cannot be recognized without a doubt.

DE 40 25 400 C1 has a method and probe arrangement for the DK-compensated kapa zitive level measurement to the object. The probe arrangement consists of a filling level measuring probe and a compensation probe. The level measuring probe and compen sation probe extend over the entire product height. For level measurement the absolute measuring capacities of the level measuring probe and compensation probe, which with a level-independent correction value, which is based solely on the dielectric depends on the total value of the product used. The probes are designed so that the level-dependent capacity values can be measured in a container-neutral manner.

DE 40 37 927 A1 describes a device for stepwise level measurement, in which Capacitors are arranged along a filling section. The capacities of the condenser Ren can be influenced by a dielectric formed by a medium. The condens with the same dielectric, capacitors have approximately the same capacitance and are in arranged at least two groups, the capacitors of a group in Füllstrec ken direction alternately in parallel are assigned to two sub-groups. For every Group gives a comparison unit depending on the difference of the resulting Capacities of their subgroups a digital output signal.

In DE-OS 22 21 741 a device for capacitive measurement of the local La described by separating layers between two adjacent media. For this several capacitors are arranged at a distance and the change in capacitance  the capacitors will enter through between the electrodes of the capacitors determined the media. The two identical structures follow each other at a distance the capacitors have electrodes and gal connected to a common connection vanically separated counter electrodes. The common connection is on an impulse generator connected, with the galvanically isolated counter electrodes connected to the inputs be connected to a differential amplifier.

The published patent application DE 197 13 267 A1 has a method for determining the Dielek Tricity constant and / or the conductivity of at least one medium and a pre direction to carry out the procedure on the subject. The method is suitable for Determination of the location of a boundary layer between two media of different dielectric con constant and / or conductivity and can even under very difficult external conditions such as increased pressure and elevated temperature a safe and trouble-free enable digital or analog display. According to this procedure, the complex Impedance of at least one of the electrodes arranged on a probe and a Ge gene electrode and / or the conductivity between at least one arranged on the probe Neten electrode and a counter electrode measured.

Presentation of the invention

With the solution proposed according to the invention, compensation occurs parasitic capacities reached over aging and temperature. Furthermore, one can fogging due to precipitation or icing of a section of the Definitely recognize the level sensor. Through constant monitoring and investigation parasitic capacitances such. B. that of the carrier substrate to which the liquid supplied electrodes on the opposite side can be added individually or in pairs a capacitance variation due to temperature penetrated into the carrier substrate ner liquid and a change in capacity due to the life span. With the method proposed according to the invention can without significant additional wall to create a criterion, which is also a clear choice the fogging / icing of the level sensor.

The electrodes picked up on the sides of a carrier substrate can e.g. B. as Electrode pairs can be formed, the comb-shaped individual electrodes of one another are otherwise trained. By short-circuiting the individual electrodes of the electrodes pairs, a single electrode can be formed on each side of the carrier substrate  whose capacitance measurements the capacitance of the carrier substrate lying between them can be determined. Since the geometry of the carrier substrate is generally known, However, the electricity constant can be determined or the influence can develop the expected parasitic capacities.  

The electrodes - be they single electrodes or pairs of electrodes - on the sides of the Trä gersubstrates, can differ both per side in the same amount and per side in Licher height be formed, d. H. in different lengths over the sides of the Trä gersubstrates be arranged extending.

If the electrodes are of identical height, an improvement in the achieve absolute measurement accuracy, in which case a signal with respect to a fogging or icing has occurred.

Will the electrodes or electrode pairs hang on both sides of the carrier substrate trained in different heights, resulting from the height difference of the Electrodes, a stray field. After determining the total capacities on each side of the Carrier substrates individually and subsequent difference formation between the total Kapa is the height difference between the electrodes or pairs of electrodes allocable additional capacity known. From the known geometry of the additional capacity can be a maximum capacity in air or in the medium, its level determine is win.

If the level sensor procured in this way occurs fogging or Icing occurs, a very high additional capacity occurs, which a plausibility monitor measurement signal of the level sensor is allowed because the air or in the medium, whose level is to be measured, the maximum additional capacity occurring is known and for a comparison is available.

During normal operation, electrodes are located opposite one another on the carrier sub strat shorted. Switching between short-circuiting the elec trode or the short-circuiting of opposing electrodes, as mentioned above, can be made very easily via an evaluation circuit, which, for. B. at An applications in motor vehicles anyway on the central control unit or ASIC of a burn engine already exists.

drawing

The invention is described in more detail below with reference to the drawing.  

It shows:

Fig. 1 is a level sensor structure in perspective view

Fig. 2 the level sensor with folded into the plane of the drawing shown pairs of comb-like intermeshing individual electrodes of different lengths.

variants

The illustration of FIG. 1 is given a level sensor structure in perspective view supported tener side view. The carrier substrate 1 of a capacitive level sensor has a first side surface 2 and a second side surface 3 . The longitudinal edge of the carrier substrate is identified by reference number 4 ; the upper edge of the carrier substrate 1 is identified by the reference symbol 5 . The lower edge opposite the upper edge 5 is designated by reference number 6 . The perspective view of the first side surface 2 of the carrier substrate 1 shows a first pair of electrodes 7 . The first pair of electrodes 7 comprises two intermeshing individual electrodes 8 and 9 . The individual electrodes 8 and 9 have connections 10 and 11 , respectively, with which the first individual electrode 8 and the second individual electrode 9 of the first pair of electrodes 7 are connected to an evaluation circuit (see illustration according to FIG. 2, evaluation circuit 28 ).

The first individual electrode 8 and the second individual electrode 9 each comprise in the longitudinal direction of the carrier substrate 1 , ie parallel to the longitudinal edge 4 extending longitudinal conductor 15 , from which comb-configured tines 12 and 13 branch off at regular intervals. The distance between the prongs 12 of the first individual electrode 8 and the prongs 13 of the second individual electrode 9 is dimensioned such that identical distances between the individual prongs 12 and 13 , the first individual electrode 8 and the second individual electrode 9 occur in the vertical direction the first side surface 2 of the carrier substrate 1 . The carrier substrate can have the cuboid configuration shown in FIG. 1, and other geometries of the carrier substrate 1 are also conceivable. The carrier substrate is made of materials such. B. ceramic or plastic.

On the second side surface 3 of the carrier substrate 1 , which does not appear from the perspective view as shown in FIG. 1, a further pair of electrodes is taken up, which strates in an identical structure to the second side surface of a carrier substrate 1 and in an identical position to the first Electrode pair 7 , comprising individual electrodes 8 and 9 , extends on the first side surface 2 of the carrier substrate 1 .

Fig. 2 shows the level sensor with folded into the plane of the drawing shown pairs of comb-like intermeshing electrodes of different length.

The representation according to Fig. 2, the first pair of electrodes 7 and another, the second electrode pair that is, 18 of the first side surface 2 and the second side surface 3 of the carrier substrate 1 can be removed, said first pair of electrodes 7 and the second Elek folded into the drawing plane trodenpaar 18 shown are. The first pair of electrodes 7 , the first single electrode 8 and the second single electrode 9 comprising, is formed in a he most height 23 . From the illustration according to Fig. 2 reveals that the terminal 10 of the first individual electrode 8 and the terminal 11 of the second Einzelelek trode 9 are connected via lines to the input side of an evaluation circuit 28th The connection 21 of a third individual electrode 19 and a connection 22 of a further, fourth individual electrode 20 are also connected via connecting lines to the input side of an evaluation circuit 28 which is only shown schematically here. The evaluation circuit 28 shown in block diagram form in FIG. 2 can be connected to the internal combustion engine of a motor vehicle, for. B. controlling central electronics and is not a separate component in connection with the present invention. Via the evaluation circuit 28 , as indicated in FIG. 2, the individual connections 10 , 11 , 21 , 22 of the individual electrodes 8 , 9 , 19th or 20 of the first pair of electrodes 7 or further, ie the second pair of electrodes 18 , are short-circuited in various circuit configurations.

The further, ie second electrode pair 18 folded into the plane of the drawing in FIG. 2 comprises a third individual electrode 19 and a further, ie fourth individual electrode 20 . The two individual electrodes 19 and 20 of the second pair of electrodes 18 intermesh like a comb and each comprise a longitudinal conductor 15 provided with a connection 21 or with a further connection 22 , of which the prongs 12 and 13 already mentioned in connection with FIG. 1 branch horizontally. Between the prongs 12 and 13 of the individual electrodes 19 and 20 , a constant height distance 16 is formed. The third individual electrode 19 and the further, ie fourth individual electrode 20 , which make up the further, ie second pair of electrodes 18 on the carrier substrate 1 , are embodied in a second overall height 24 which corresponds to the first overall height 23 of the first pair of electrodes 7 as shown in FIG. 2 exceeds.

If the individual electrodes 8 or 9 of the first pair of electrodes 7 and the individual electrodes, ie the third individual electrode 19 and the further, ie fourth individual electrode 20 of the second pair of electrodes 18 are of the same overall height 23 or 24 , there is no stray field region 26 on the carrier substrate 1 , as in connection with Fig. 2 Darge.

When forming the first pair of electrodes 7 and the second pair of electrodes 18 in different heights 23 and 24 , however, the stray field region 26 shown in FIG. 2 results. The overall height difference 25 between the first pair of electrodes 7 and the second pair of electrodes 18 is known.

According to the proposed method, the evaluation circuit 28 first short-circuits the first individual electrode 8 and the second individual electrode 9 of the most electrode pair 7 on the first side surface 2 of the carrier substrate 1 . Furthermore, the third individual electrode 19 and the further, ie the fourth individual electrode 20 of the second pair of electrodes 18 are short-circuited. Short-circuiting the individual electrodes arranged on the first side surface 2 or on the second side surface 3 results in an individual electrode on each side. A subsequent capacitance measurement between the first side surface 2 and the second side surface 3 of the carrier substrate 1 results in the capacitance of the carrier substrate 1 . Since the geometry of the carrier substrate 1 is known, its dielectric constant can be determined, or a parasitic capacitance can be determined. This can be calculated out during a measurement, ie it does not falsify the measurement results of the electrode pairs 7 or 18 on the first side surface 2 or the second side surface 3 . The resulting stray field region 26 - in the example according to FIG. 2 in the upper region of the first side face 2 of the carrier substrate 1 - is assumed to be negligible in comparison to the total capacitance, or is known if there is no fogging / icing.

The short-circuiting of the individual electrodes 8 and 9 on the first side surface 2 of the carrier substrate 1 by means of the evaluation circuit 28 is indicated by the broken line 30 ; The same applies to the dashed line 30 between the connecting lines, which is indicated at the connections 21 , 22 of the longitudinal conductor 15 of the third individual electrode 19 or the further, ie fourth individual electrode 20 of the second pair of electrodes 18 .

According to the method proposed by the invention by switching the evaluation device 28 in a next step, the capacitance between the individual electrodes 8 , 9 of the first pair of electrons 7 and in a further process step according to the proposed method by means of the evaluation circuit 28, the capacitance between the third individual electrode 19 and of the fourth individual electrode 20 of the second pair of electrodes 18 is measured. Accordingly, the total capacitance of each side of the carrier substrate 1 , ie on the first side surface 2 and the second side surface 3, is determined in this method step. An additional capacitance results from a difference between the determined total capacity on the first side surface 2 and the second side surface 3 . The additional capacity can be determined from the height difference 25 with respect to the construction heights 23 and 24 of the individual electrodes of the first pair of electrodes 7 and the second pair of electrodes 18 . The additional capacity corresponding to the height difference is that which corresponds to a maximum capacity in air or in the medium, the fill level of which is to be determined by means of the capacitive fill level sensor proposed according to the invention. The value of the additional capacitance 7 is known from the geometry of the materials and is available in the evaluation circuit 28 as a comparison value. If there is fogging or icing of a partial area of the level sensor, this will preferably occur in its upper area, since it is assumed that the lower area above the lower edge 6 always remains surrounded by fluid; therefore there is a high additional capacity, which significantly exceeds the reference additional capacity. The deviation of the actually measured value of the additional capacity, which results due to the loading or icing of an upper portion of the level sensor, can be done with the reference value stored in the evaluation circuit 28 for the additional capacity, based on the capacity determination in air or for the medium surrounding the sensor was determined, are compared. A plausibility criterion is thus available which allows a statement to be made about the fogging / icing fault, ie if, from a comparison of the value of the additional capacity, in a reference state, ie surrounded by air or medium, with an actual fault due to a fault, such as e.g. , B. the formation of fogging or icing is the maximum additional capacity value that far exceeds the reference value.

In normal operation, that is to say a level measurement by means of the capacitive level sensor, the evaluation circuit 28 indicates the first of the third individual electrodes 19 opposite one another on the carrier substrate 1 , indicated by reference symbol 29 or the first individual electrode 8 and the fourth individual electrode 20 - likewise indicated by the short circuit Reference numeral 29 - shorted together.

It should also be mentioned that when the first pair of electrodes 7 or the second pair of electrodes 18 are made at the same height 23 or 24, a stray field region 26 , as shown in FIG. 2, does not arise and a fogging warning due to the lack of a difference in height between the Electrode pairs resulting additional capacity is not output. The individual electrodes 8 and 9 of the first pair of electrodes 7 and the individual electrodes 19 and 20 of the second pair of electrodes 18 in the same overall height, however, provide an improvement in the absolute measurement accuracy, since the stray field region 26 , as shown in FIG Electrode pairs 7 and 18 in the same height would be zero.

With the solution according to the invention, a time-consuming measurement of the parasitic capacitances before installation and the assumption of a constant parasitic carrier capacitance of the carrier substrate 1 can be avoided. The assumption of a constant parasitic carrier substrate capacity has proven to be unsustainable since the parasitic capacitance of the carrier substrate 1 changes as a function of age. However, the assessment of the change in capacity via temperature and a mathematical compensation of the same does not record this age drift. With the method proposed according to the invention, in particular when the individual electrodes 8 or 9 of the first pair of electrodes 7 are designed in a different overall height 23 than the individual electrodes 19 or 20 of the second pair of electrodes 18 in a further overall height 24 , a plausibility of the measurement signal with regard to the occurrence can be achieved of fogging or freezing so that with the existing method, for. B. when used on internal combustion engines an untight cylinder head gasket could be detected, which causes droplets of water to enter the oil pan, which can be reliably detected by a considerable increase in the additional capacity.

LIST OF REFERENCE NUMBERS

1

carrier substrate

2

first side surface

3

second side surface

4

longitudinal edge

5

top edge

6

lower edge

7

first pair of electrodes

8th

first single electrode

9

second single electrode

10

Connection of the first single electrode

11

Connection of a second single electrode

12

Tine first single electrode

13

Tine second single electrode

14

comb arrangement

15

longitudinal conductor

16

height distance

17

lateral distance

18

second pair of electrodes

19

third single electrode

20

fourth single electrode

21

Connection of third single electrode

22

Fourth single electrode connection

23

Height of first pair of electrodes

24

Height of the second pair of electrodes

25

Height difference Δ

26

Stray field area

27

Material thickness substrate

28

evaluation

29

Short circuit in normal operation

30

Short circuit per side surface

2

.

3

Claims (8)

1. Method for determining fogging or icing of level transmit capacitive level sensors with the following method steps:

• - On side surfaces ( 2 , 3 ) of a carrier substrate ( 1 ) recorded individual electrodes ( 8 , 9 ; 19 , 20 ) are short-circuited in pairs;
• the capacitance of the carrier substrate ( 1 ) is determined on the basis of a measurement of the capacitance between the side surfaces ( 2 , 3 ),
• - The capacitance between the individual electrodes ( 8 , 9 ; 19 , 20 ) of a first pair of electrodes ( 7 ) is measured on the first side surface ( 2 ) and the capacitance between the individual electrodes ( 8 , 9 ; 19 , 20 ) is measured two pairs of electrodes ( 18 ) on the second side surface ( 3 ) of the carrier substrate ( 1 ) individually,
• - By forming the difference in the capacities of the side surfaces ( 2 , 3 ), a height difference Δ ( 25 ) corresponding additional capacity is determined, which corresponds to a maximum capacity in air or in the medium, the level of which is to be detected, and this is compared with a subjected to the actually measured value of the additional capacity.

2. The method according to claim 1, characterized in that by means of an evaluation circuit ( 28 ), the individual electrodes ( 8 , 9 ; 19 , 20 ) on the first and second Seitenflä surface ( 2 , 3 ) of the carrier substrate ( 1 ) are short-circuited, whereby Individual electrodes are formed on the first and second side surfaces ( 2 , 3 ) of the carrier substrate ( 1 ). 3. The method according to claim 1, characterized in that during the level measurement in each case a single electrode ( 8 , 9 ) of the first pair of electrodes ( 7 ) on the first side surface ( 2 ) with a single electrode ( 19 , 20 ) of the second pair of electrodes ( 18 ) is short-circuited on the second side surface ( 3 ) of the carrier substrate ( 1 ). 4. The method according to claim 1, characterized in that with a different overall height ( 23 , 24 ) of the individual electrodes ( 8 , 9 ; 19 , 20 ) and the electrode pairs ( 7 , 18 ), a stray field region ( 26 ) on the surfaces ( 2 , 3 ) of the carrier substrate ( 1 ) occurs. 5. The method according to claim 4, characterized in that on the first side surface ( 2 ) the capacitance between the individual electrodes ( 8 , 9 ) of the first pair of electrodes ( 7 ) and on the second side surface ( 3 ) the capacitance between the individual electrodes ( 19 , 20 ) of the second pair of electrodes ( 18 ) is measured individually on the sides of the carrier substrate ( 1 ). 6. The method according to claim 4, characterized in that a level measurement between the first individual electrode ( 8 ) and the third individual electrode ( 19 ) is carried out and the second individual electrode ( 9 ) with the fourth individual electrode ( 20 ) is short-circuited in normal operation. 7. Device for performing the method according to one or more of claims 1 to 6, each containing individual electrodes ( 8 , 9 ; 19 , 20 ), the surfaces on the sides (2, 3) of the carrier substrate ( 1 ) are arranged and can be connected by means of an evaluation circuit ( 28 ) to a first pair of electrodes ( 7 ) or a second pair of electrodes ( 18 ), characterized in that the individual electrodes ( 8 , 9 ; 19 , 20 ) on the side surfaces ( 2 , 3 ) of the Carrier substrates ( 1 ) have different heights ( 23 , 24 ) per side surface ( 2 , 3 ). 8. The device according to claim 7, characterized in that the individual electrodes ( 8 , 9 ) of the first pair of electrodes ( 7 ) on the first side surface ( 2 ) of the carrier substrate ( 1 ) and the individual electrodes ( 19 , 20 ) of the second pair of electrodes ( 18 ) the second side surface ( 3 ) of the carrier substrate ( 1 ) can be short-circuited and individual electrodes ( 8 , 9 ; 19 , 20 ) of the first and second pair of electrodes opposite one another on the first and second side surfaces ( 2 , 3 ) of the carrier substrate ( 1 ) ( 7 , 8 ) can be short-circuited.